Organometallics XXXX, XXX, 000–000 A DOI: 10.1021/om900498m

Infrared Spectra of Small Insertion and Methylidene Complexes in Reactions of Laser-Ablated Nickel Atoms with

Han-Gook Cho,† Lester Andrews,*,‡ Bess Vlaisavljevich,§ and Laura Gagliardi§,^ †Department of Chemistry, University of Incheon, 177 Dohwa-dong, Nam-ku, Incheon, 402-749, South Korea, ‡Department of Chemistry, University of Virginia, P.O. Box 400319, Charlottesville, Virginia 22904-4319, §Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455-0431, and ^Department of Physical Chemistry, University of Geneva, 30, q. E. Ansermet, 1211 Geneve, Switzerland

Received June 12, 2009

Nickel carbene complexes, CX2dNiX2, are prepared along with the insertion products, CX3-NiX, in reactions of laser-ablated Ni atoms with tetrahalomethanes. These reaction products are identified from matrix infrared spectra and density functional frequency calculations. In agreement with the previously studied Pt cases, the carbon-nickel bonds of the Ni carbene complexes are essentially double bonds with CASPT2-computed effective bond orders of 1.8-1.9. On the other hand, only insertion complexes are generated from and precursors. The nickel carbenes have staggered structures, and several insertion complexes containing C-Cl bonds reveal distinct bridged structures similar to those observed in the corresponding Fe products, which indicate effective coordination of Cl to the metal center. The unique F-bridged CH2F-NiCl structure is also observed.

Introduction actinides with small alkanes and halomethanes via C-H(X) insertion following H(X) migration.5-9 These complexes High oxidation-state complexes, first introduced in the also show distinct structures, particularly due to agostic 1 1970s, are now considered an essential part of coordination interaction and dramatic photochemical reactions including chemistry and help to understand the nature of carbon-metal photoreversibility. Their small sizes make them ideal for 2 bonds. Their rich chemistry includes growing applications in high-level theoretical approaches and, therefore, are consid- numerous syntheses including metathesis, catalytic properties, ered as model systems for their much larger cousins. The 3 and C-H insertion. Their distinct structures and photoche- higher oxidation-state complexes, however, are expected to mical properties have also provided testing grounds for be less favored on going far right among the transition metals 4 theoretical applications. in the periodic table because the d-orbital becomes more Recently small high-oxidation-state complexes have been filled. reported from reactions of group 3-8 transition metals and More recently small Pt carbene complexes, along with the

Publication Date (Web): September 9, 2009 | doi: 10.1021/om900498m insertion products, have been identified in reactions with *To whom correspondence should be addressed. E-mail: lsa@ 10 - Downloaded by UNIV DE GENEVA on September 9, 2009 | http://pubs.acs.org and halomethanes. The C Pt bond orders com- virginia.edu. (1) (a) Fischer, E. O.; Kreis, G.; Kreiter, C. G.; Muller,€ J.; Huttner, puted by density functional theory and natural bond order G.; Lorenz, H. Angew. Chem., Int. Ed. Engl. 1973, 12, 564. (b) Schrock, R. range from 1.41 to 1.70 as Cl is replaced by F since the R. J. Am. Chem. Soc. 1974, 96, 6796. more electronegative evidently supports a stronger (2) (a) Herndon, J. W. Coord. Chem. Rev. 2009, 253, 1517. carbon-metal bond. The small Pt methylidenes have a (b) Herndon, J. W. Coord. Chem. Rev. 2009, 253, 86. (c) Herndon, J. W. - Coord. Chem. Rev. 2007, 251, 1158. (d) Herndon, J. W. Coord. Chem. Rev. substantial amount of double bond character from dπ pπ 2006, 250, 1889. (e) Herndon, J. W. Coord. Chem. Rev. 2005, 249, 999. bonding, and their C-Pt bonds are considerably shorter (f) Herndon, J. W. Coord. Chem. Rev. 2004, 248, 3, and earlier review articles in this series. (3) (a) Crabtree, R. H. Chem. Rev. 1995, 95, 987, and references (6) (a) Cho, H.-G.; Andrews, L. J. Phys. Chem. A 2007, 111, 2480. therein. (b) Wada, K.; Craig, B.; Pamplin, C. B.; Legzdins, P; Patrick, B. O.; (b) Cho, H.-G.; Andrews, L. Organometallics 2007, 26, 633. (Group 3). Tsyba, I.; Bau, R. J. Am. Chem. Soc. 2003, 125, 7035. (c) Ujaque, G.; (7) (a) Cho, H.-G.; Andrews, L. Organometallics 2007, 26, 4096. Cooper, A. C.; Maseras, F.; Eisenstein, O.; Caulton, K. G. J. Am. Chem. Soc. (b) Cho, H.-G.; Andrews, L. Inorg. Chem. 2008, 47, 1653. (Re). 1998, 120, 361. (8) (a) Cho, H.-G.; Lyon, J. T.; Andrews, L. Organometallics 2008, (4) Clot, E.; Eisenstein, O. In Computational Inorganic Chemistry; 27, 5241. (b) Cho, H.-G.; Andrews, L. Eur. J. Inorg. Chem. 2008, 2537. Kaltzoyannis, N., McGrady, J. E., Eds.; Structure and Bonding; Spring- (c) Cho, H.-G.; Andrews, L. Organometallics 2008, 27, 1786. (Group 8). er: Heidelberg, 2004; pp 1-36. Aubert, C.; Buisine, O.; Malacria, M. Chem. (9) (a) Andrews, L.; Cho, H.-G. J. Phys. Chem. A 2005, 109, 6796. Rev. 2002, 102, 813, and references therein. (b) Cho, H.-G.; Lyon, J. T.; Andrews, L. J. Phys. Chem. A 2008, 112, 6902. (5) (a) Andrews, L.; Cho, H.-G. Organometallics 2006, 25, 4040, and (c) Lyon, J. T.; Cho, H.-G.; Andrews, L. Eur. J. Inorg. Chem. 2008, 1047 references therein (review article, groups 4-6). (b) Lyon, J. T.; Cho, H.-G.; (Actinides). Andrews, L. Organometallics 2007, 26, 2519 (Ti, Zr, Hf þ CHX3,CX4). (10) (a) Cho, H.-G.; Andrews, L. J. Am. Chem. Soc. 2008, 130, 15836. (c) Lyon, J. T.; Cho, H.-G.; Andrews, L. Organometallics 2007, 26, 6373 (b) Cho, H.-G.; Andrews, L. J. Phys. Chem. A 2008, 112, 12293. (c) Cho, (Cr, Mo, W þ CHX3,CX4). H.-G.; Andrews, L. Organometallics, 2009, 28, 1358. (Pt).

r XXXX American Chemical Society pubs.acs.org/Organometallics B Organometallics, Vol. XXX, No. XX, XXXX Cho et al.

than those of typical Pt(II) carbene complexes, leading to a conclusion that the small Pt methylidene complexes have substantial Pt(IV) character.11 As a continuation of our investigation on the chemistry of small transition-metal high-oxidation-state complexes, we re- port reactions of Ni with halomethanes. In contrast to the case of Pt,10 which is considered as the most effective C-H insertion agent among group 10 metals,10,12 only tetrahalomethanes generate Ni methylidenes. Several insertion products have interesting structures, particularly due to intermolecular inter- action between X bonded to C and the metal center.

Experimental and Computational Methods

Laser-ablated nickel atoms were reacted with CCl4 (Fisher), 13 CCl4 (90% enriched, MSD Isotopes), CFCl3,CF2Cl2 (Dupont), CHCl3,CH2Cl2,CH2FCl, CH2F2 (Dupont), CDCl3, 13 CD2Cl2 (MSD Isotopes), CD2FCl, and CD2F2 (synthesized )in excess argon during condensation at 10 K using a closed-cycle refrigerator (Air Products Displex). These methods have been described in detail in previous publications.10,14 Reagent gas - mixtures were in the range 0.2 1.0% in argon. The Nd:YAG - -1 laser fundamental (1064 nm, 10 Hz repetition rate, 10 ns pulse Figure 1. Infrared spectra in the 1000 800 cm region for the width) was focused on a rotating metal target (Ni, 99.99%, reaction products of the laser-ablated nickel atom with CCl4 iso- Johnson Matthey) using 5-10 mJ/pulse. After initial reaction, topomers in excess argon at 10 K. (a) Ni and CCl4 (0.5% in argon) -1 λ infrared spectra were recorded at 0.5 cm resolution using a co-depositedfor1h.(b)As(a)aftervisible( > 420 nm) irradiation. Nicolet 550 spectrometer with a Hg-Cd-Te range B detector. (c) As (b) after ultraviolet (240-380 nm) irradiation. (d) As (c) after Then samples were irradiated for 20 min periods by a mercury arc full arc (λ > 220 nm) irradiation. (e) As (d) after annealing to 26 K. 13 street lamp (175 W) with the globe removed using a combination (f) Ni and CCl4 reagent (0.5% in argon) co-deposited for 1 h. (g-j) of optical filters or annealed to allow further reagent diffusion. As (f) spectra taken following the same irradiation and annealing To provide support for the assignment of new experimental sequence. i and m designate the product absorption groups, while - frequencies and to correlate with related works,5 10 density func- P and c stand for the precursor and common absorptions. tional theory (DFT) calculations were performed using the Gauss- ian 03 program system,15 the B3LYP and BPW91 density and the optimized geometry was confirmed by vibrational analysis. functionals,16,17 and the 6-311þþG(3df,3pd)basissetsforC,F,Cl, The vibrational frequencies were calculated analytically, and zero- and Ni atoms.18 Geometries were fully relaxed during optimization, point energy is included in the calculation of binding and reaction energies. Previous investigations have shown that DFT-calculated harmonic frequencies are usually slightly higher than observed (11) Prokopchuk, E. M.; Puddephatt, R. J. Organometallics 2003, 22, frequencies,5-10,19 and they provide useful predictions for infrared 563, and references therein. Pt(IV). spectra of new molecules. Natural bond orbital (NBO) analysis15,20 (12) (a) Carroll, J. J.; Weisshaar, J. C.; Siegbahn, P. E. M.; Wittborn, - C. A. M.; Blomberg, M. R. A. J. Phys. Chem. 1995, 99, 14388. (b) Low, J. was done to help understand the carbon nickel bonding in the J.; Goddard, W. A.III. Organometallics 1986, 5, 609. (c) Wang, X.; Andrews, carbenes, but the results were questionable, and the carbenes were L. J. Phys. Chem. A 2004, 108, 4838. (d) Cho, H.-G.; Andrews, L. J. Phys. examined using CASSCF/CASPT2 methods and triple-ζ (ANO- Chem. A 2004, 108, 6272. RCC-VTZP) basis sets.21,22 An active space of (6,6) was chosen for (13) Isotopic modifications synthesized: Andrews, L.; Willner, H.; the active orbitals involved in the C-M bond. A CASPT2 Prochaska, F. T. J. Chem. 1979, 13, 273.

Publication Date (Web): September 9, 2009 | doi: 10.1021/om900498m geometry optimization was performed for the carbenes starting (14) (a) Andrews, L.; Citra, A. Chem. Rev. 2002, 102, 885, and from DFT geometries. The orbitals shown below and the occupa-

Downloaded by UNIV DE GENEVA on September 9, 2009 | http://pubs.acs.org references therein. (b) Andrews, L. Chem. Soc. Rev. 2004, 33, 123, and references therein. tion numbers used to compute the effective bond orders (EBO = (15) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; bonding minus antibonding electons divided by two) are from the Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; final calculation at the optimized geometry. A quadruple-ζ Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; CASPT2 optimization was performed on Cl2Ni-CCl2 to confirm Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, that the triple-ζ basis was sufficient. G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, Results and Discussion C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Reactions of nickel atoms with halomethanes were inves- Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; tigated, and infrared spectra (Figures 1-6) and quantum Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; (19) (a) Scott, A. P.; Radom, L. J. Phys. Chem. 1996, 100, 16502. Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, (b) Andersson, M. P.; Uvdal, P. L. J. Phys. Chem. A 2005, 109, 3937. M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; (20) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88, Pople, J. A. Gaussian 03, Revision C.02; Gaussian, Inc.: Wallingford, CT, 899. 2004. (21) (a) Roos, B. O. The Complete Active Space Self-Consistent Field (16) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang, Method and its Applications in Electronic Structure Calculations. In Y.; Parr, R. G. Phys. Rev. B 1988, 37, 785. Advances in Chemical Physics; Ab Initio Methods in Quantum Chemis- (17) (a) Becke, A. D. Phys. Rev. A 1988, 38, 3098. (b) Burke, K.; try-II; Lawley, K. P., Ed.; John Wiley & Sons Ltd.: New York, 1987; Perdew, J. P.; Wang, Y. In Electronic Density Functional Theory: Recent Chapter 69, p 399. (b) Andersson, K.; Malmqvist, P.-A˚.; Roos, B. O. Progress and New Directions; Dobson, J. F., Vignale, G., Das, M. P. Ed.; J. Chem. Phys. 1992, 96, 1218 as implemented in Molcas 7.4. Plenum, 1998. (22) Roos, B. O.; Lindh, R.; Malmqvist, P.-A˚.; Veryazov, V.; Widmark, (18) Raghavachari, K.; Trucks, G. W. J. Chem. Phys. 1989, 91, 1062. P.-O. J. Phys. Chem. A, 2005, 109, 6575. (ANO-RCC-VTZP) basis. Article Organometallics, Vol. XXX, No. XX, XXXX C

Figure 3. Infrared spectra in the 1000-450 cm-1 region for the reaction products of the laser-ablated nickel atom with CHCl3 isotopomers in excess argon at 10 K. (a) Ni and CHCl3 (0.5% in argon) co-deposited for 1 h. (b-e) As (a) spectra taken following the irradiation and annealing sequence described in Figure 1 caption (visible, UV, and full arc irradiations and annealing to - - -1 Figure 2. Infrared spectra in the 1350 800 and 550 450 cm 26 K). (f) Ni and CDCl3 reagent (0.5% in argon) co-deposited regions for the reaction products of the laser-ablated nickel for 1 h. (g-i) As (f) spectra taken following a sequence of visible atom with CF2Cl2 and CFCl3 in excess argon at 10 K. (a) Ni and UV irradiation and annealing to 34 K. i, P, and c stand for - and CF2Cl2 (0.5% in argon) co-deposited for 1 h. (b e) As product, precursor, and common absorptions, respectively. (a) spectra taken following the irradiation and annealing se- quence described in Figure 1 caption (visible, UV, and full arc irradiations and annealing to 26 K). (f) Ni and CFCl3 reagent (0.5% in argon) co-deposited for 1 h. (g-j) As (f) spectra taken following the same irradiation and annealing sequence. Notice the photoreversible intensity variation of the m absorptions in the CFCl3 spectra (decrease and increase on visible and UV irradiations). i and m designate the product absorption groups, while P and c stand for the precursor and common absorptions. chemical frequency calculations of the products and their structures (Figures 7, 8) will be presented in turn. Ni þ CX4. Laser-ablated Ni atoms co-deposited with in excess argon during condensation at 10 K produced two strong new absorptions at 953.3 cm-1 (944.0 cm-1 satellite for matrix site splitting) and 912.2 cm-1 -1 Publication Date (Web): September 9, 2009 | doi: 10.1021/om900498m (909.9 cm shoulder for isotopic splitting) (labeled -1

Downloaded by UNIV DE GENEVA on September 9, 2009 | http://pubs.acs.org m for methylidene). Previously reported bands at 1036.4 cm þ 23 -1 24 -1 (CCl3 ), 1019.3 and 926.7 cm (Cl2CCl-Cl), and 898 cm 25 (CCl3) were also observed: these are common to all laser- ablated metal experiments with CCl4 as produced by ablation plume photolysis, and their identification follows from earlier work using vacuum ultraviolet irradiation.23 -1 The product absorptions increased in concert 5, 20, and a few Figure 4. Infrared spectra in the 1100-410 cm region for the % on sequential irradiations in the visible (λ > 420 nm), reaction products of the laser-ablated nickel atom with CH2Cl2 ultraviolet (240-380 nm), and full arc (λ > 220 nm) regions, isotopomers in excess argon at 10 K. (a) Ni and CH2Cl2 (0.5% in 13 argon) co-deposited for 1 h. (b-e) As (a) spectra taken following respectively. A similar experiment with CCl4 (90% enriched) shifted the new absorptions to 920.5 cm-1 (912.6 cm-1 satellite) the irradiation and annealing sequence described in Figure 1 - caption (visible, UV, and full arc irradiations and annealing to (12/13 isotopic frequency ratio of 1.0356) and to 883.2 cm 1 -1 26 K). (f) Ni and CD2Cl2 reagent (0.5% in argon) co-deposited (880.8 cm shoulder) (12/13 ratio of 1.0328). The appearance - 12 -1 for 1 h. (g i) As (f) spectra taken following a sequence of visible of a weak C product band at 953.3 cm with about 1/10 of and UV irradiation and annealing to 28 K. the 13C product band absorbance (Figure 1) confirms that a single carbon atom participates in these vibrational modes. The -1 -1 (23) (a) Jacox, M. E.; Milligan, D. E. J. Chem. Phys. 1971, 54, 3935. 909.9 and 880.8 cm shoulders on the 912.2 and 883.2 cm (b) Jacox, M. E. Chem. Phys. 1976, 12, 51. (c) Prochaska, F. T.; Andrews, L. þ bands are 6/9 of the main band absorbances, which is appro- J. Chem. Phys. 1977, 67, 1091. (CCl3 ) priate for natural abundance chlorine isotopes in a species (24) Maier, G.; Reisenauer, H. P.; Hu, J.; Hess, B. A., Jr.; Schaad, L. J. Tetrahedron Lett. 1989, 30, 4105. (Cl CCl-Cl). containing two equivalent chlorine atoms (statistical popula- 2 35 37 35 (25) Andrews, L. J. Chem. Phys. 1968, 48, 972. (CCl3). tion of one Cl and one Cl vs two Cl atoms). D Organometallics, Vol. XXX, No. XX, XXXX Cho et al.

Figure 5. Infrared spectra in the 1200-500 cm-1 region for the reaction products of the laser-ablated nickel atom with CH2FCl isotopomers in excess argon at 10 K. (a) Ni and CH2FCl (0.5% in argon) co-deposited for 1 h. (b-e) As (a) spectra taken following the irradiation and annealing sequence described in Figure 1 caption (visible, UV, and full arc irradiations and annealing to 26 K). (f) Ni and CD2FCl reagent (0.5% in argon) co-deposited for 1 h. (g-j) As (f) spectra taken following the same sequence. i, P, and c stand for product, precursor, and common absorptions, respectively.

Figure 7. Structures calculated for the identified reaction pro- ducts of nickel with halomethanes at the B3LYP level of theory using the 6-311þþG(3df,3pd) basis sets for H, C, F, Cl, and Ni. Bond distances and angles are in A˚and deg. Notice the staggered allene-type structures of the Ni methylidenes and the bridged structures of the insertion complexes [the bridged halogen-metal distance is given in brackets]. Molecular symmetries are given under each structure. Publication Date (Web): September 9, 2009 | doi: 10.1021/om900498m Downloaded by UNIV DE GENEVA on September 9, 2009 | http://pubs.acs.org

Figure 6. Infrared spectra in the 1000-450 cm-1 region for the reaction products of the laser-ablated nickel atom with CH2F2 isotopomers in excess argon at 10 K. (a) Ni and CH2F2 (0.5% in argon) co-deposited for 1 h. (b-e) As (a) spectra taken following Figure 8. Calculated CASPT2 structures for the nickel carbenes. the irradiation and annealing sequence described in Figure 1 5-10 caption (visible, UV, and full arc irradiations and annealing to and halomethanes, they are assigned to the symmetric - 26 K). (f) Ni and CD2F2 reagent (0.5% in argon) co-deposited and antisymmetric CCl2 stretching modes of CCl2 NiCl2. for 1 h. (g-j) As (f) spectra taken following the same sequence. i, The carbon 12/13 isotopic frequency ratio for a pure sym- P, and c stand for product, precursor, and common absorptions, metric CCl2 stretching mode is smaller than that for an respectively. antisymmetric stretching mode, but mixing with the Ni-C stretching mode increases the carbon participation and the The two strong m product absorptions in the C-Cl 12/13 isotopic frequency ratio, as found for the CCl2-PtCl2 stretching region suggest that a primary product with a molecule.10a This mode is in fact C vibrating back and CCl2 moiety is generated during co-deposition of the laser- forth between Ni and two Cl atoms in an antisymmetric ablated nickel atoms and CCl4. On the basis of our previous fashion. The totally symmetric counterpart calculated at experience for reactions of metal atoms with hydrocarbons 451.9 cm-1 (Table 1) has a very small carbon-13 shift, as Article Organometallics, Vol. XXX, No. XX, XXXX E

1 a Table 1. Observed and Calculated Fundamental Frequencies of CCl2-NiCl2 Isotopomers in the A1 Ground State in C2v Symmetry

12 35 35 13 35 35 C Cl2-Ni Cl2 C Cl2-Ni Cl2 approximate description obsb B3LYPc intc BPW91c intc obsb B3LYPc intc BPW91c intc

A1 C-Cl2,Ni-C str. 953.3 945.2 248 958.2 196 920.5 912.7 231 925.0 182 B2 CCl2 str. 912.2 899.9 233 863.0 209 883.2 871.0 218 835.3 196 B1 NiCCl2 deform 452.4 6 453.7 7 431.8 24 410.2 2 A1 Ni-C, C-Cl2 str. 451.9 1 425.5 4 451.5 1 453.6 7 B1 NiCl2 str. 443.4 70 453.6 57 447.7 52 453.3 58 A1 NiCl2 str. 343.3 3 348.9 4 343.2 3 348.6 4 A1 NiCl2, CCl2 bend 244.6 0 241.3 1 244.5 0 241.1 1 B2 Cl2NiCCl2 def 194.9 0 191.4 0 194.3 0 190.8 0 B2 CNiCl2 def 106.6 4 103.5 2 106.5 4 103.4 2 A1 NiCl2 bend 92.1 3 96.5 0 92.0 3 96.4 0 B1 NiCl2 rock 57.6 1 69.1 1 57.6 1 69.1 1 A2 CCl2 twist 14.5 0 19.2 0 14.5 0 19.2 0 a Frequencies and intensities are in cm-1 and km/mol. Approximate mode descriptions as considerable mixing is involved. The first and fourth modes differ by phasing of the C motion, antisymmetric for the first and symmetric for the fourth mode. b Observed in an argon matrix. Chlorine isotopic splitting listed. c Harmonic frequencies and intensities computed with B3LYP or BPW91/6-311þG(3df).

Table 2. Observed and Calculated Fundamental Frequencies of triplet state is energetically comparable (0.6 kcal/mol lower) - 1 a CCl3 NiCl Isotopomers in the A Ground State to the singlet state; however, the CCl2 frequencies calculated for the triplet state are much lower (e.g., the B3LYP fre- 12 - 13 - - - CCl3 NiCl CCl3 NiCl quencies of 862.5 and 839.9 cm 1 are 90.8 and 72.3 cm 1 approximate lower than the observed values) and the predicted isotopic description obsb B3LYPc intc obsb B3LYPc intc shifts (27.3 and 27.4 cm-1) are not in good agreement as well. 0 On the basis of the observed frequencies and their isotopic A CCl2 s. str. 851.3 862.9 143 824.2 833.0 132 00 d d A CCl2 as. str. 798.0 166 772.2 156 shifts, which are in excellent agreement with the predicted 0 A NiCCl2 deform 463.2 29 458.9 27 values, the Ni methylidene product has a singlet ground A0 C-Ni str. 432.0 110 426.9 96 0 state. A NiCl2 as. str. 383.7 20 378.4 27 0 Recently small Pt carbenes have been formed in reactions A NiCl2 s. str. 290.4 5 290.3 4 00 A CCl2 scis. 236.3 0 235.6 0 with methane and halomethanes and observed in the matrix 0 A Cl2NiC deform 229.3 13 229.2 13 infrared spectra. The C-Pt bond is clearly a double bond 0 A NiCl2 wag 165.4 33 164.8 33 00 and apparently much stronger than those in larger Pt com- A NiCl2 bend 148.6 1 148.5 1 10,11 00 plexes. Previous studies reveal that higher oxidation- A NiCl2 rock 78.2 2 78.2 2 A0 CCl twist 76.4 4 76.4 4 state transition-metal complexes are favored on going down 2 5-8,12 a -1 b the family, and therefore, Ni is normally considered a Frequencies and intensities are in cm and km/mol. Observed in - an argon matrix. c Frequencies and intensities computed with B3LYP/ weaker C H(X) insertion agent than Pt. Our identification 6-311þG(3df) are for harmonic calculations. d Covered by precursor of CCl2-NiCl2 from reactions of CCl4 isotopomers, how- absorption. CCl3-NiCl has a bridged Cs structure. Attempts to opti- ever, confirms that Ni also undergoes C-X insertion and mize with BPW91/6-311þG(3df) end up with the methylidene structure following X migration from C to Ni. - (CCl2 NiCl2). Another weak product absorption marked “i”(i for insertion) is observed at 851.3 cm-1 and its 13C counterpart -1 -1 Publication Date (Web): September 9, 2009 | doi: 10.1021/om900498m the carbon atom hardly moves in this mode. The 912.2 cm at 824.2 cm (12/13 ratio of 1.0329). They decrease slightly - Downloaded by UNIV DE GENEVA on September 9, 2009 | http://pubs.acs.org band is due to the antisymmetric C Cl2 stretching mode, on visible irradiation, but increase slightly on UV irradia- and the 1.0328 isotopic 12/13 frequency ratio is virtually the tion. The frequency and 13C shift indicate that it is a C-Cl 10a same as found for the CCl2-PtCl2 molecule. stretching band of another product formed in the reaction of 5-10 The observed CCl2 stretching frequencies correlate well Ni and CCl4. The previous studies and computational with the predicted values for CCl2-NiCl2 in its singlet results suggest that the most plausible product along with the ground state as shown in Table 1, and the carbon-13 isotopic methylidene complex is the insertion complex, CCl3-NiCl. shifts are also well reproduced (observed 32.8 and 29.0 cm-1 The insertion complex is expected to have a bridged structure vs predicted 32.5 and 28.9 cm-1). The observed frequencies (Figure 7) and to be energetically comparable to the methy- are, however, slightly higher than the predicted values, and lidene complex (1.8 kcal/mol lower). The observed frequency similar reversals are also observed from the C-X stretching and 13C shift are in good agreement with the predicted values frequencies in the previously studied halogenated late transi- for the CCl2 symmetric stretching mode of the insertion tion-metal carbene and carbynes.8,10 The two strong ob- complex (862.9 and 27.1 cm-1) as shown in Table 2. Un- served (antisymmetric and symmetric) CCl2 stretching fortunately the antisymmetric CCl2 stretching band and its absorptions and their 13C counterparts are consistent with 13C counterpart are believed to be covered by precursor the DFT results and substantiate formation of the Ni absorption, and other bands are calculated to be too weak methylidene, CCl2-NiCl2, via C-Cl bond insertion by Ni to observe. We tentatively assign the weak i absorption to the and subsequent Cl migration from C to Ni. CCl2 symmetric stretching mode of the insertion complex in Unfortunately the weaker NiCl2 antisymmetric stretching the singlet ground state. The singlet and triplet states are band is predicted too close to our observation limit, and all energetically close again (66.0 and 63.5 kcal/mol more stable the other vibrational bands of the Ni methylidene are too than the reactants), but the triplet insertion complex would weak to be observed (Table 1). It is also notable that the have the CCl2 symmetric and strongest antisymmetric F Organometallics, Vol. XXX, No. XX, XXXX Cho et al.

1 1 00 a Table 3. Observed and Calculated Fundamental Frequencies of CF2-NiCl2 and CFCl-NiCl2 in the A2 and A Ground States

CF2-NiCl2 CFCl-NiCl2 approximate approximate description obsb B3LYPc intc BPW91c intc description obsb B3LYPc intc BPW91c intc

0 A1 CF2 s. str. 1310.0 1328.1 501 1279.1 528 A C-F str. 1251.9 1269.1 274 1207.6 283 0 B2 CF2 as. str. 1294.5 1302.8 242 1213.7 217.5 A C-Cl str. 974.8 966.2 363 946.1 295 0 A1 CF2 bend 726.4 15 705.7 4 A CFCl bend 540.3 2 538.7 6 00 B1 CF2 wag 520.8 579.5 59 546.7 24 A NiCFCl deform 474.5 508.1 25 480.2 7 00 B1 NiCl2 as. str. 451.9 69 453.9 55 A NiCl2 as. str. 448.9 69 453.1 58 0 A1 NiCl2 s. str. 387.2 1 416.6 3 A C-Ni str. 360.8 3 372.2 5 0 A1 C-Ni str. 334.6 0 336.3 0 A NiCl2 s. str. 324.8 0 324.7 0 0 B2 CF2 rock 274.1 0 277.9 0 A CFCl rock 214.4 0 214.0 0 0 A1 NiCl2 bend 117.8 5 116.4 3 A NiCl2 wag 112.5 4 111.1 2 0 B2 NiCl2 wag 88.4 7 93.4 2 A NiCl2 bend 88.5 5 94.2 1 00 A2 CCl2 twist 21.4 2 56.9 1 A NiCl2 rock 42.5 2 64.5 0 00 B1 NiCl2 rock -8.0 0 -36.6 0 A CFCl twist -9.5 0 -13.7 0 a Frequencies and intensities are in cm-1 and km/mol. b Observed in an argon matrix. c Frequencies and intensities computed with B3LYP or BPW91/ 6-311þG(3df) are for harmonic calculations. CF2-NiCl2 and CFCl-NiCl2 have staggered allene-type C2v and Cs structures. - Table 4. Observed and Calculated Fundamental Frequencies of with the B3LYP frequency of 1181.0 cm 1 for the C-F - 1 a CFCl2 NiCl in the A Ground States stretching mode of the insertion complex, CFCl2-NiCl (Table 4). Another i absorption at 868.6 cm-1 (with a - - CFCl2 NiCl shoulder at 866.5 cm 1) is assigned to the C-Cl stretching approximate mode. The products from C-Cl insertion are much more b c c c c description obs B3LYP int BPW91 int stable than those via C-F insertion; CFCl-NiCl2, - - - C-F str. 1119.8 1181.0 225 1210.0 279 CCl2 NiFCl, CFCl2 NiCl, and CCl3 NiF are 63, 48, 62, C-Cl str. 868.6, 866.5 892.9 242 945.3 294 and 49 kcal more stable than the reactants, respectively. CFCl bend 533.4 52 537.8 6 CFCl2-NiCl has a C1 structure with a bridging Cl atom NiCFCl deform 474.6 93 479.8 6 similar to CCl3-NiCl as shown in Figure 7. NiCl2 as. str. 441.0 53 453.7 59 C-Ni str. 330.2 6 371.6 6 Again the triplet states are energetically comparable; the NiCl s. str. 291.0 10 325.1 0 singlet and triplet states for the Ni methylidenes are 63 and 2 3 CFCl rock 245.7 5 213.3 0 64 kcal/mol more stable than the reactant (Ni( F) þ CFCl3). NiCl2 wag 166.3 1 113.3 2 Optimization attempts for the triplet insertion complex also NiCl2 bend 140.3 47 96.1 1 end up with the triplet methylidene. However, the triplet NiCl2 rock 90.1 4 68.5 0 - CFCl twist 77.2 4 19.0 0 methylidene would have its C Cl stretching and NiCFCl deformation bands at ∼850 and ∼410 cm-1, which are not a Frequencies and intensities are in cm-1 and km/mol. b Observed in an argon matrix. c Frequencies and intensities computed with B3LYP or observed in this study. Most probably the F-containing Ni BPW91/6-311þG(3df) are for harmonic calculations. CFCl2-NiCl has methylidene is in its singlet ground state (Table 3). a bridged C1 structure. In the CF2Cl2 spectra the m absorptions remain unchanged on visible irradiation but increase ∼15% and another ∼5% on stretching band at ∼790 and ∼720 cm-1, which are not UV and full arc photolysis. The two strong m absorptions at observed from the spectra. -1 -1 -1 1310.0 cm (with a satellite at 1315.1 cm ) and 1294.5 cm Ni þ CFCl and CF Cl . Infrared spectra from the reaction -1 26 3 2 2 (with a satellite at 1297.9 cm )intheC-F stretching region of Ni atoms with the chlorofluoromethanes are shown in Publication Date (Web): September 9, 2009 | doi: 10.1021/om900498m reflect formation of a primary product with a CF2 group, most Figure 2. In the CFCl3 spectra three m absorptions are - Downloaded by UNIV DE GENEVA on September 9, 2009 | http://pubs.acs.org probably CF NiCl . The observed CF stretching bands are observed, which decrease one-third and double on visible and 2 2 2 assigned to the symmetric and antisymmetric modes of the Ni UV irradiations reversibly. The two strong product absorp- methylidene, and the frequencies are well reproduced as tions, one at 1251.9 cm-1 (with a satellite at 1244.3 cm-1)inthe 26 -1 shown in Table 3. A weak m absorption is also observed at C-F stretching region and the other one at 974.8 cm in the -1 520.8 cm and assigned to the CF wagging mode. The C-Cl stretching region, indicate that a primary product with a 2 tetrahalomethanes (CCl ,CFCl,andCFCl ) used in this CFCl group is generated in the process of co-deposition and 4 3 2 2 study all produce the Ni carbene complexes via C-Cl inser- subsequent UV photolysis. It is most likely CFCl-NiCl ,and 2 tion following Cl migration from C to Ni. The observed the observed C-FandC-Cl stretching frequencies are well vibrational characteristics show that CF -NiCl is also in reproduced by computation as shown in Table 3. The weak 2 2 the singlet ground state because the triplet state would have absorption at 474.5 cm-1 is assigned to the NiCFCl deforma- the symmetric and antisymmetric CF2 stretching bands tion mode. All other bands are either too weak to observe or -1 at ∼1250 and ∼1200 cm and the CF2 wagging band at beyond our observation limit. The observed bands and good -1 ∼420 cm , while the singlet and triplet states are 60 and correlation with the predicted values support formation of the 63 kcal/mol, respectively, more stable than the reactants. F-containing Ni methylidene. No i absorption is observed in the CF Cl spectra, unlike Parallel to the Ni þ CCl case, weak i absorptions are also 2 2 4 the CCl and CFCl cases. It is, however, in line with the fact observed, which increase ∼20% on UV photolysis. The one 4 3 that attempts to optimize the structure of the insertion at 1119.8 cm-1 in the C-F stretching region is compared complex all end up with that of CF2-NiCl2, suggesting that the original C-Cl bond insertion directly leads to Cl migra- (26) Pavia, D. L.; Lampman, G. M.; George, S. K. Introduction to tion from C to Ni to form the methylidene complex in Spectroscopy, 3rd ed.; Brooks Cole: New York, 2000. reaction of Ni with CF2Cl2. The products with Ni-Cl bonds Article Organometallics, Vol. XXX, No. XX, XXXX G

1 0 a Table 5. Calculated Fundamental Frequencies of CHCl2-NiCl Isotopomers in the A Ground State

CHCl2-NiCl CDCl2-NiCl approximate description obsb B3LYPc intc BPW91c intc obsb B3LYPc intc BPW91c intc C-H str. 3162.8 3 3084.5 2 2327.2 2 2269.4 1 C-H ip. bend 1233.0 22 1180.5 20 882.3 931.9 90 892.1 111 C-H oop. bend 935.1 995.1 33 945.2 49 763.8 819.2 45 788.9 69 C-Cl str. 803.1 805.3 128 779.0 163 671.3 727.2 46 698.2 49 CNiCl s. str. 601.5 19 606.5 16 560.1 35 559.8 26 CNiCl as. str. 472.9 471.7 63 440.0 12 457.2 40 436.8 13 Ni-Cl str. 422 428.8 67 421.0 102 420 426.3 71 409.6 87 CClNi s. str. 290.3 2 285.9 2 288.9 2 284.7 2 CClNi as. str. 223.3 2 225.0 2 222.9 2 224.5 2 CNiCl ip. bend 186.8 6 179.2 5 185.0 5 177.6 4 Ni-Cl oop. bend 97.9 3 98.6 2 97.1 3 97.7 2 Ni-Cl ip. bend 77.9 3 76.0 3 77.8 3 75.9 3 a Frequencies and intensities are in cm-1 and km/mol. b Observed in an argon matrix. c Frequencies and intensities computed with B3LYP or BPW91/ 6-311þþG(3df, 3pd) are for harmonic calculations. CHCl2-NiCl has a bridged C1 structure.

1 a Table 6. Observed and Calculated Fundamental Frequencies of CH2Cl-NiCl Isotopomers in the A Ground States

.CD2Cl-NiCl approximate description obsb B3LYPc intc BPW91c intc obsb B3LYPc intc BPW91c intc 00 A CH2 as. str. 3211.8 0 3136.9 0 2392.6 0 2337.5 0 0 A CH2 s. str. 3106.3 2 3029.8 3 2246.4 2 2189.6 3 0 A CH2 scis. 1426.3 2 1373.7 2 1059.5 4 1022.1 4 0 A CH2 wag 1031.1 1080.8 11 1031.3 12 813.1 851.3 8 816.3 8 00 A CH2 twist 988.8 0 946.9 0 728.2 0 700.2 0 A0 CClNi s. str. 700.0 696.0 28 709.7 24 645.0 639.8 39 648.2 33 00 A CH2 rock 680.1 6 658.9 5 502.9 3 485.6 2 A0 CClNi as. str. 496.8 511.4 25 493.1 19 477.3 489.8 11 473.9 6 A0 NiCl str. 425 426.2 58 426.4 51 422 424.4 59 423.2 52 A0 CClNi bend 240.2 1 244.1 1 239.3 1 243.3 1 A00 CNiCl oop bend 104.4 3 103.6 1 103.1 3 102.6 1 A0 CNiCl ip bend 101.9 5 97.6 4 100.1 5 95.9 4 a Frequencies and intensities are in cm-1 and km/mol. b Observed (i absorption) in an argon matrix. c Frequencies and intensities computed with B3LYP or BPW91/6-311þþG(3df, 3pd) are for harmonic calculations. CH2Cl-NiCl has a bridged Cs structure in its triplet ground state.

are far more stable than those with Ni-F bonds. For example, methylidenes are the primary products. Chlorine migration CF2-NiCl2 and CFCl-NiFCl are 60 and 42 kcal/mol more from C to Ni in the insertion complex is evidently more stable than the reactants. It is consistent with the fact that the difficult than the tetrahalomethane cases, and the insertion Ni-F stretching absorptions, which would be strong and near complex is also marginally more stable than the methylidene -1 650 cm , are not observed in the CFCl3 and CF2Cl2 spectra. product: CHCl2-NiCl and CHCl-NiCl2 in their singlet

Publication Date (Web): September 9, 2009 | doi: 10.1021/om900498m Ni þ CHCl3. Figure 3 shows the infrared spectra from ground states are 60 and 53 kcal/mol more stable than the 3 þ - Downloaded by UNIV DE GENEVA on September 9, 2009 | http://pubs.acs.org reactions of Ni with CHCl3 and CDCl3, where the product reactants (Ni( F) CHCl3). Triplet CHCl2 NiCl is again absorptions are weaker relative to the tetrahalomethane cases. energetically comparable (2.6 kcal/mol higher) to the sing- The product absorptions (all marked with “i”) arise from the let insertion product, but its CNiCl2 deformation bands insertion complex, based on comparison with computed would appear with similar intensities at ∼720, ∼520, and frequencies (Table 5). These bands increase ∼50% on visible ∼480 cm-1, which are not observed in this study. irradiation but decrease ∼20 and ∼10% on the following UV Ni þ CH2X2. Figures 4-6 are the spectra from reactions of -1 and full arc photolysis. The i absorption at 935.1 cm and D Ni with CH2Cl2,CH2FCl, and CH2F2 and their deuterated -1 counterpart at 793.6 cm (H/D ratio of 1.178) are assigned to isotopomers. Parallel to the CHCl3 case, the insertion com- the C-H(C-D) out-of-plane bending mode. The relatively plexes are the primary products, and no m absorptions are strong i absorption at 803.1 cm-1 has its D counterpart at observed, correlating well with the stability of the insertion 671.3 cm-1 (H/D ratio of 1.196) and is designated as the C-Cl complex relative to the carbene product in each case. -1 stretching mode. The weak absorption at 472.9 cm with its CH2Cl-NiCl(S), CH2F-NiCl(T), and CH2F-NiF(T) are D counterpart at 450.1 cm-1 (H/D ratio of 1.051) is assigned 18, 2, and 11 kcal/mol more stable than the Ni carbene to the CNiCl antisymmetric stretching mode. The one at counterparts, respectively. 882.3 cm-1 from the deuterated product is assigned to the Figure 4 shows the product spectra from reactions of Ni C-D in-plane bending mode, while its H counterpart expec- and CH2Cl2 isotopomers, where the i absorptions remain ted at ∼1180 cm-1 is probably covered by precursor absorp- unchanged on visible irradiation but increase ∼5% on UV tion. The observed i absorptions substantiate formation of the irradiation and increase slightly further on full arc photo- Ni insertion complex in reaction with CHCl3. lysis. The insertion complex is believed to have a Cs structure The absence of the m absorptions in the CHCl3 spectra is with a bridging Cl atom (Figure 7), and the weakened C-Cl in contrast to the tetrahalomethane cases, where the Ni bond, due to coordination to the metal center, leads to a low H Organometallics, Vol. XXX, No. XX, XXXX Cho et al.

1 a Table 7. Observed and Calculated Fundamental Frequencies of CH2F-NiCl Isotopomers in the A Ground States

CH2F-NiCl CD2F-NiCl approximate description obs B3LYP int BPW91 int obs B3LYP int BPW91 int

CH2 as. str. 3197.3 1 3117.6 1 2384.1 1 2325.3 1 CH2 s. str. 3086.0 6 3004.2 7 2229.9 5 2169.2 7 CH2 scis. 1456.0 0 1402.8 0 1087.2 10 1049.1 9 CH2 wag 1122.0 1177.2 29 1127.0 31 884.2 949.8 17 917.2 20 CH2 twist 1137.1 3 1093.4 3 856.2 2 825.3 2 C-F str. 844.9 889.7 131 874.4 119 797.7 848.9 132 824.7 126 CH2 rock 678.9 7 657.0 6 571.0 3 557.1 5 C-Ni str. 605.3, 598.4 629.8 12 614.2 20 501.4 4 485.0 3 Ni-Cl str. 425.3 434.0 44 435.2 31 433.4 44 434.7 31 NiCF bend 242.3 6 223.2 5 241.5 6 222.4 6 CH2F tort 122.5 5 117.9 4 118.8 5 113.9 3 CNiCl bend 105.1 10 101.4 9 102.2 10 98.7 9 a Frequencies and intensities are in cm-1 and km/mol. b Observed (i0 absorption) in an argon matrix. c Frequencies and intensities computed with B3LYP or BPW91/6-311þþG(3df, 3pd) are for harmonic calculations. CH2F-NiCl has a bridged C1 structure in its triplet ground state.

3 a Table 8. Observed and Calculated Fundamental Frequencies of CH2F-NiCl Isotopomers in the A Ground States

CH2F--NiCl CD2F-NiCl approximate description obsb B3LYPc intc BPW91c intc obsb B3LYPc intc BPW91c intc

CH2 as. str. 3110.7 9 3046.9 7 2308.4 5 2260.8 4 CH2 s. str. 3022.1 13 2943.4 11 2188.1 9 2130.1 8 CH2 scis. 1446.4 5 1391.1 3 1073.6 22 1036.2 33 CH2 twist 1209.1 8 1167.1 3 901.1 2 872.0 2 CH2 wag 1158.2 1207.1 70 1146.7 48 900.6 949.2 48 899.7 88 C-F str. 982.6 969.2 239 952.8 238 956.7 942.6 203 926.4 138 C-Ni str. 602.7 11 573.3 8 507.5 17 490.2 7 CH2 rock 537.2 24 506.4 13 455.5 35 431.8 26 Ni-Cl str. 388.8 54 388.7 32 378.4 36 371.6 15 FCNi bend 164.9 6 176.0 3 163.2 6 173.5 3 CNiF bend 78.6 5 83.8 3 74.7 5 80.2 4 CH2F tort 30.1 8 39.6 5 29.5 8 38.6 5 a Frequencies and intensities are in cm-1 and km/mol. b Observed in an argon matrix. c Frequencies and intensities computed with B3LYP or BPW91/ 6-311þþG(3df, 3pd) are for harmonic calculations. CH2F-NiCl has a bridged C1 structure in its triplet ground state.

stretching frequency. The i absorption at 1031.1 cm-1 along are observed. The i absorptions remain unchanged upon with the D counterpart at 813.1 cm-1 (H/D ratio of 1.268) is visible and UV irradiation, but decrease ∼20% on full arc 0 assigned to the CH2 wagging mode. Another one at 700.0 irradiation, whereas the i absorptions increase ∼20% on cm-1 shows a D shift of -55.0 cm-1 (H/D ratio of 1.085) and visible irradiation, remain almost the same on UV irradia- is assigned to the C-Cl 333Ni symmetric stretching mode on tion, and decrease slightly on full arc irradiation. The

Publication Date (Web): September 9, 2009 | doi: 10.1021/om900498m the basis of the frequency and relatively small D shift. The observed frequencies are compared with the DFT frequen- -1 -1 -1

Downloaded by UNIV DE GENEVA on September 9, 2009 | http://pubs.acs.org one at 496.8 cm has its D counterpart at 477.3 cm (H/D cies in Tables 7 and 8. The i absorption at 1122.0 cm along - ratio of 1.041) and is assigned to the C-Cl 333Ni antisym- with its D counterpart at 884.2 cm 1 (H/D ratio of 1.268) is -1 metric stretching mode. The strong absorption at 425 cm assigned to the CH2 wagging mode of singlet CH2F-NiCl on near our observation limit shows its D counterpart at 422 the basis of the frequency and small D shift. The strong i cm-1 and is assigned to the Ni-Cl stretching mode. The four absorption at 844.9 cm-1 has its D counterpart at 797.7 cm-1 observed i absorptions and their D counterparts have good (H/D ratio of 1.059) and is assigned to the C-F stretching correlations with the DFT frequencies and substantiate mode of the bridged (C-F 333Ni) complex in the singlet state -1 formation of CH2Cl-NiCl. (Figure 7). Another i absorption at 605.3 cm (with a -1 In addition, isolated NiCl2 is observed at 520.9, 517.5, and shoulder at 598.4 cm ) is assigned to the C-Ni stretching 513.1 cm-1 (Figure 4) for chlorine and nickel isotopic splittings, mode without observation of the D counterpart. The weak 27 -1 in good agreement with previous observations. Such NiCl2 absorption at 425 cm (not shown) is tentatively assigned to bands were detected with CCl4 but not with CHCl3.The the Ni-Cl stretching mode. The observed absorptions all observation of NiCl2 suggests that CH2-NiCl2 may be formed support formation of singlet, F-bridged CH2F-NiCl in these experiments, but if so, it decomposes. The strong (Table 7). The strongest Ni-F stretching absorption for -1 425 cm band is not appropriate for assignment to either the Ni methylidene, CH2-NiFCl, would be expected at singlet- or triplet-state carbene based on calculated frequencies. ∼650 cm-1 in both singlet and triplet states, which is not The spectra from reactions of CH2FCl and its deuterated observed in this study. isotopomer are shown in Figure 5, where i and i0 absorptions The i0 absorption at 1158.2 cm-1 has its D counterpart at -1 900.6 cm (H/D ratio of 1.286), and we assign it to the CH2 (27) Jacox, M. E.; Milligan, D. E. J. Chem. Phys. 1969, 51, 4143. wagging mode of the insertion complex in the triplet state - (NiCl2). (CH2F NiCl(T)) on the basis of the frequency, H/D ratio, Article Organometallics, Vol. XXX, No. XX, XXXX I

and computational results. The strong i0 absorption at 982.6 cm-1 with its D counterpart at 956.7 cm-1 (H/D ratio of 1.027) is assigned to the C-F stretching mode (Table 8). The structure of the insertion complex in the triplet state substantially differs from that in the singlet state, while the singlet and triplet states are almost isoergic (42 and 43 kcal 3 lower than the reactants (Ni( F) þ CH2FCl)). Unlike the F-bridged structure in the singlet state, it does not bear a bridged structure and the C-Ni-Cl moiety is more linear (—CNiCl = 145.0), and therefore, the large structural difference is retained by trapping in the matrix and so is the electronic state. Unfortunately all other bands for CH2F-NiCl(T) are expected to be too weak to observe as shown in Table 8. Figure 6 illustrates spectra from reaction of Ni with CH2F2 and CD2F2, where only one type of absorption marked “i0” is observed. The product absorptions decrease slightly on visible irradiation, increase ∼30% on UV photo- lysis, and increase slightly further on full arc photolysis. We attribute these product absorptions to the insertion product in its triplet ground state (i0 for triplet insertion complex). The i0 absorption at 958.3 cm-1 (with a shoulder at 955.8 cm-1) has its D counterpart at 927.1 cm-1 (H/D ratio of 1.034) and is assigned to the C-F stretching mode on the basis of the frequency and small D shift. The strong absorp- tion at 663.7 cm-1 along with its D counterpart at 657.0 cm-1 (H/D ratio of 1.010) is assigned to the Ni-F stretching mode. The weaker i0 absorption at 573.2 cm-1 has its D counterpart at 484.0 cm-1 (H/D ratio of 1.184) and is assigned to the 0 CH2 rocking mode. Another i absorption is observed at -1 927.0 cm in the CD2F2 spectra, and its H counterpart is believed covered by precursor absorption. It is assigned to the CH2 wagging mode. The carbene complex (CH2-NiF2) is 15 and 11 kcal/mol higher in the singlet and triplet states than the insertion complex and would show the strong NiF2 antisymmetric stretching band at ∼750 cm-1, which is not observed. The singlet insertion complex (4.5 kcal/mol higher than that in the triplet state) would have the strong C-F stretching band at ∼830 cm-1 and its D counterpart at ∼790 cm-1, which are not observed in the spectra. Structures of Ni Complexes. The calculated structures of the Ni complexes identified here are illustrated in Figure 7.

Publication Date (Web): September 9, 2009 | doi: 10.1021/om900498m The carbene complexes, CCl2-NiCl2, CFCl-NiCl2, and - Downloaded by UNIV DE GENEVA on September 9, 2009 | http://pubs.acs.org CF2 NiCl2, have staggered structures, parallel to the corre- sponding group 8 metal and Pt complexes.8,10 The B3LYP- computed C-Ni bond lengths of the small Ni carbenes of 1.733, 1.738, and 1.748 A˚are slightly longer than CASPT2 values, 1.673, 1.663, and 1.658 A˚, which may be compared with those of 1.83-1.92 A˚for typical Ni carbenes.28 The CASPT2 structures for the carbenes are shown in Figure 8. New CASSCF/CASPT2 calculations were performed on the carbenes in order to characterize the nickel-carbon bonds. The molecular orbitals involved in the C-Ni bonds are illustrated in Figure 9. The EBO, effective bond orders (bonding minus antibonding occupancy divided by two), of - - - CCl2 NiCl2, CFCl NiCl2, and CF2 NiCl2 are 1.81, 1.84, Figure 9. Calculated CASPT2 orbitals involved in the carbon- and 1.87 as shown. Analogous calculations reveal 1.89, 1.90, nickel double bonds. Occupation numbers given in parentheses. and 1.91 EBO values for the corresponding Pt complexes. In agreement with the previously characterized group 3-8 metal, actinide, and Pt carbenes,5-10 the methylidene C-Ni bond is essentially a double bond. The increasing effective (28) (a) Miki, K.; Taniguchi, H.; Kai, Y.; Kasai, N.; Nishiwaki, K.; bond order with the number of F atoms is also observed in Wada, M. J. Chem. Soc., Chem. Commun. 1982, 1180. (b) Hou, H.; previously studied Pt systems,10 suggesting that the more Gantzel, P. K.; Kubiak, C. P. J. Am. Chem. Soc. 2003, 125, 9564. (c) Normand, A. T.; Hawkes, K. J.; Clement, N. D.; Cavell, K. J.; Yates, electronegative F substituent on carbon contracts the C 2p B. F. Organometallics 2007, 26, 5352 (C-Ni length). orbitals and thus enhances the C 2p-Ni 3d orbital overlap. J Organometallics, Vol. XXX, No. XX, XXXX Cho et al.

The Ni insertion complexes with X (particularly Cl) through C-X bond activation/insertion followed by R-X bonded to C have bridged structures as shown in Figure 7, transfer,8-10 reaction 1. and similar bridged structures (with bridging Cl) are ob- M þCX4 f CX3-MX f CX2-MX2 f CX-MX3 served in the Fe insertion complexes CH2Cl-FeCl and 8 CHCl2-FeCl. Coordination of Cl electrons to the metal ð1Þ center is evidently more efficient than that of F, and The present results reveal that C-X bond insertion by CH2F-NiCl is believed to be the first F-bridged complex between C and M to the best of our knowledge. Coordina- group 10 metal atoms occurs readily in reactions with tion of F electrons to Ni is, however, not as effective as that of halomethanes, and in the case of tetrahalomethanes, Cl; the —FCNi (79.3) is larger than those of the Cl-bridging X migration from C to M also follows. However, further complexes (—ClCNi = 71.9-76.7), and vibrational analysis X migration to form the carbyne product has not been shows that the contribution of the Ni 333F stretching motion observed, probably due to the much higher energy of the - to the C-F stretching mode is insignificant. product. For example, CCl PtCl3 is 27 kcal/mol higher in d 10 As described above, the singlet and triplet states of the energy than CCl2 PtCl2, and geometry optimization for CCl-NiCl and CCl-PdCl results in the corresponding identified products except CH2F-NiF are almost isoergic; 3 3 however, the observed vibrational characteristics correlate carbene complexes. with those predicted for the singlet states. In the case of Conclusions CH2F-NiCl, evidence shows that both the singlet and triplet states are trapped in a matrix as described above. It is not clear at the moment why the singlet Ni products are more Laser-ablated Ni atoms react with halomethanes, and the favored in the matrix. The singlet Ni products are in line with products are identified on the basis of isotopic shifts and - the identified singlet Pt complexes.10 Unlike the Ni cases, the correlation with the DFT results. The CX2 NiX2 molecules singlet states of the Pt products are substantially more stable are produced by reactions with tetrahalomethanes, revealing than the triplet states. that group 10 metals all form carbenes, while the reaction is more exothermic and the yield much higher for X = Cl than Reactions. Previous studies and the present results reveal 10 that high-oxidation-state complexes are generated from X = F, parallel to the previously studied Pt case. On the reactions of group 3-10 transition metals and actinides with other hand, only insertion complexes are identified from small alkanes and halomethanes.5-10,29 However, the pre- reactions with precursors containing H substituents, indicat- - ference for methylidene products in reactions of group 10 ing that X migration from C to M following initial C X bond metals varies substantially. Pt, which is regarded in general insertion becomes much more difficult. This also suggests that as the strongest insertion agent among group 10 metals,12 group 10 metals are close to the limit where the carbene forms carbenes not only with haloalkanes but with less complex is no longer produced in transition-metal reactions reactive methane as well.10 Analogous Ni carbene complexes with halomethanes. In agreement with the Pt case, the car- - are, on the other hand, far less favored. They are produced bon metal bonds of the Ni carbenes are essentially double - only in reactions with tetrahalomethanes, thanks to the bonds with effective bond orders in the range 1.8 1.9. - Although singlet states are clearly the most stable for the preference for reaction of the M X bond (particularly the 10 M-Cl bond) over the M-H bond. Only the insertion corresponding Pt complexes, DFT calculations show that complex is formed with and dihalomethane the singlet and triplet states are often nearly isoergic for the precursors. It is possible that repulsion between halogen Ni complexes. However, the observed vibrational character- atoms on the carbon center in the insertion product increases istics show that most of the Ni products also have singlet the rate of R-X transfer. Overall these results suggest that ground states. The identified Ni carbene complexes all have group 10 metals are near the limit of carbene complex staggered structures, whereas the insertion products with a - Publication Date (Web): September 9, 2009 | doi: 10.1021/om900498m formation in reactions with small alkanes and halomethanes, C Cl bond have bridged structures, indicative of efficient Cl electron donation to the metal center. CH2F-NiCl reveals a

Downloaded by UNIV DE GENEVA on September 9, 2009 | http://pubs.acs.org which is consistent with the fact that Ni carbene complexes 2 unique F-bridged structure. are rare. The observation of NiCl2 in the CH2Cl2 experi- ments suggests that the CH2-NiCl2 carbene may be formed but decomposes. Acknowledgment. We gratefully acknowledge financial Investigations in our laboratory have shown that laser- support from National Science Foundation (U.S.) Grant ablated transition-metal atoms react with halomethanes CHE 03-52487 to L.A., and support from Korea Institute of Science and Technology Information (KISTI) by Grant (29) Cho, H.-G.; Andrews, L. Reactions of group 9 metals with No. KSC-2008-S02-0001 and from the Swiss National halomethanes, unpublished data. Science Foundation (grant 200020-120007).